3T3-F442A fibroblasts which differentiate to adipocytes spontaneously produce and secrete interferon (IFN) in a transient manner which is related to specific stages of growth and differentiation. This system provides a means to examine the role of IFN and the IFN-induced protein kinase (dsI) during growth and differentiation. The overall objective of the proposed studies is to determine if IFN is an important biological signal for differentiation. The specific aims include: (1) determining the level and type of IFN produced in differentiating and non-differentiating clones of 3T3 cells and the effect of IFN on adipose differentiation and induction of dsI; (2) defining the functional role of dsI during growth and differentiation with emphasis on protein synthesis regulation by phosphorylation and the mechanism of dsI activation in vivo; (3) examining the role of IFN/dsI in other biological systems. The methods include: culturing of differentiating and non-differentiating clones of 3T3 cells to examine effects on growth and differentiation; nucleic acid hybridization and immunologic techniques to quantitate levels of IFN and dsI; protein phosphorylation and protein synthesis assays to examine activation and activity of IFN and dsI in vivo and in vitro. Recombinant DNA techniques will be used to prepare cDNA probes to dsI-mRNA. IFNs elicit a spectrum of biological responses in normal and tumor cells and tissues. The anti-tumor effects of IFNs make them potentially important as therapeutic agents for human cancers. These studies should provide increased understanding of the mechanisms which regulate growth and differentiation of adipose cells.